The present invention relates to an image forming method and an image forming apparatus which are utilized in electrophotographic image formation, and particularly relates to an image forming method and an image forming apparatus which are utilized in electrophotographic image formation in the field of copiers and printers.
In recent years, electrophotographic copiers and printers come to be more often utilized in printing and color printing applications. In said printing and color printing applications, digital black and white images or color images having high image quality are strongly required. For this demand, it is proposed to form a high precision digital image by use of laser light having a short wavelength as an exposure light source (Patent literature 1). However, it is a present state that an electrophotographic image finally obtained cannot achieve sufficiently high quality even when a precise electrostatic latent image is formed on an electrophotographic photoreceptor.
The reason lies in that latent image formation on an electrophotographic photoreceptor or suitable development conditions have not been made sufficiently clear and that an image forming method, which is provided with the both of precise dot latent image formation and development conditions required for toner image formation based on said dot latent image, has not been established.
That is, as an electrophotographic photoreceptor, a precise electrostatic latent image is not necessarily formed even when image exposure is performed with short wavelength laser light employing an organic photoreceptor which has been developed for short wavelength laser application, and further, in successive development, individual dot images cannot be reproduced or may be lost because a development method to independently reproduce said latent image at high density has not been sufficiently established, resulting in not achieving sufficiently precise electrophotographic image.
Further, as a development mode, particularly, as a development mode of a latent image on an organic photoreceptor, a development mode, in which a development sleeve, equipped to oppose an organic photoreceptor, proceeds in parallel to the progressive direction of an organic photoreceptor in a development section (hereinafter, referred to as a parallel development mode), and a development mode, in which the sleeve proceeds in the counter direction (hereinafter, referred to as a counter development mode) are known (Patent literature 2), however, neither of them have sufficiently solved the problems to achieve precise dot image formation.
In a development mode, in which a development sleeve, equipped to oppose an organic photoreceptor, proceeds in parallel to the progressive direction of an organic photoreceptor, developability around high density images may be deteriorated to cause density decrease, resulting in deterioration of image quality particularly with such as a high contrast photographic image.
On the other hand, in a development mode, in which the sleeve proceeds in the counter direction, developability is high to enable formation of dot images having high density, however, fog or insufficient density in the top portion is liable to be generated.
Phenomena as described above cannot be solved only by improvement of a developer, but has been proved to be emphasized or improved also depending on characteristics of an organic photoreceptor.
That is, they are related to contrast of an electrostatic latent image formed on an organic photoreceptor and generation of a reversely charged toner due to rubbing between an organic photoreceptor and a developer.
In other words, in a counter development mode, a reversely charged toner is liable to be generated by contact rubbing between an organic photoreceptor and a toner, so that fog and spattering of a toner may be caused or density decrease in the top portion is liable to be generated resulting in making reproduction of a precise electrostatic latent image as a toner image impossible.
Further, in a development mode utilizing a two-component developer, proposed has been a ferrite carrier, which makes development of a latent image on a photoreceptor soft by use of a carrier having low saturation magnetization (Patent literature 3). However, no technique to effectively apply such a soft developer into a counter development mode has been proposed.
[Patent literature 1] JP-A No. 2000-250239 (Hereinafter, JP-A refers to Japanese Patent Publication Open to Public Inspection.)
[Patent literature 2] JP-A No. 2001-125465
[Patent literature 3] JP-A No. 11-202559